equaled 0.5. It means that these water masses effected the phytoplankton bloom in
these periods weaker than in the Romanian area. In the autumn-winter period the
transformed river waters do not practically get to the Bulgarian area (Fig. 10.6).
Therefore the phytoplankton bloom in this area is mainly conditioned by the local
hydro-chemical and hydro-meteorological conditions.
1997 2000 2003 2006 2009 2012 2015
-2
-1
0
1
2
3
-1
-0.5
0
0.5
1
-1
0
1
2
1997 2000 2003 2006 2009 2012 2015
-2
-1
0
1
2
3
-1
-0.5
0
0.5
1
-1
0
1
2
-1
-0.5
0
0.5
1
-1
-0.5
0
0.5
1
1
2
3
4
T
Fig. 10.10 Inter-annual variability of the anomalies chlorophyll a concentration (C Chl ) in the
Danube region (a, b) and central (c, d) areas of the NWBS, anomalies water temperature (T w ) in
the surface water layer (e, f), and the Danube River discharge (g, h) during the winter (1), spring
(2), summer (3), and autumn (4)
10 Seasonal Changes of Hydrobiological and Bio-Optical Parameters in the. . .
175